The general principles of isobaric filling method are explained in European patent application No. EP 0 375 912. In the known isobaric method, part of the volume of a storage tank is filled with a liquid, the overlying other part being filled with a gas maintained at a pressure equal to the liquid saturation pressure. To fill a container, the container interior is put into communication with the tank via two pipes, a first of which opens into the upper part of the tank in the gas volume, whereas the second pipe opens into the lower part of the tank in liquid volume. In each pipe a shut-off valve is provided to close the relative pipe. To fill the bottle the valve of the gas pipe is opened so that the gas flows into the container. While keeping the valve of the gas pipe open, the valve of the liquid pipe is open so that the liquid falls into the container. Once reaching the filling level, the valves are stopped.
U.S. Pat. No. 6,601,618 and European patent application No. EP 1 101 998 both disclose a filling valve for the isobaric filling of a container, said filling valve having a hollow valve rod slidingly mounted in a valve housing. The valve rod is provided with a through hole defining a gas passage, and a liquid passage is defined between the outer periphery of the valve rod and the inner periphery of the housing.
These conventional filling method and filling valves require a somewhat complex network of gas and liquid pipes, provided with numerous shut-off valves which need to be precisely synchronized under control of an appropriate control device.